Mechanization of coal mining having become prevalent within about the last 50 years has virtually eliminated manual mining techniques. The greatest increase in productivity has been obtained since the late 1940's with the design and development of rotary head mining machines which use a number of bits on a rotating drum that is advanced into the coal face or reciprocated vertically to fragment the face. Two lines of evolutionary development have been pursued; one line has produced continuous mining machines characterized by wide drum type heads mounted on a yoke or boom supported on a mobile vehicle. The other line has produced a drum type machine generically termed a longwall mining machine which uses a narrower drum mounted on a single arm supporting the drum on a cantilevered shaft. The drum and support are mounted on a track adjacent the longwall.
A persistent problem encountered in mining operations is that of maintaining or increasing production while reducing generation of airborne respirable dust. U.S. Pat. No. 4,012,077, assigned to the assignee of the present invention, for example, discusses the problem of coal dust production and discloses a cutter unit having a triangular shaped drum type cutting head with cutter bits located on the apexes of the head. The head is driven in an elliptical eccentric path to cause the cutter bits to make box shaped cuts in the mine face during sump and shear cycles. In that patent, production of airborne coal dust is reduced, with an increase in productivity of coal. In U.S. Pat. No. 4,062,595, assigned to the common assignee, a method of making linear cuts in the mine face using the triangular cutting head shown in U.S. Pat. No. 4,012,077 as well as a new coal conveyor system to further reduce secondary dust generated by falling coal is disclosed. Details of the technique of linear cutting of mine faces to increase productivity and reduce production of coal dust are discussed in the two patents mentioned above and will not be repeated here for brevity; the disclosures of the two patents are incorporated herein by reference. The apparatus disclosed in these patents, however, are applicable only to continuous mining; there is no system to our knowledge for reducing coal dust production while increasing mining productivity in longwall mining machines.
One object of the present invention, therefore, is to provide a new and improved longwall mining machine capable of reducing coal dust generation while increasing productivity.
Another object is to provide a longwall mining machine using a linear cutting head undergoing eccentric rotary motion to provide deep linear cuts in a longwall face to reduce production of coal dust while increasing mining productivity.
Another object is to provide a cantilevered longwall mining machine which reduces production of coal dust by making constant depth linear cuts in a sidewall face.